The present invention relates to implements incorporating abrasive particle compacts and more particularly to a pocketed stud for receiving the abrasive particle compacts. The abrasive particle compact implements have special utility in drill bits for oil and gas exploration and in mining applications.
An abrasive particle compact is a polycrystalline mass of abrasive particles such as diamond and/or cubic boron nitride bonded together to form an integral, tough, high-strength mass. Such components can be bonded together in a particle-to-particle self-bonded relationship, by means of a bonding medium disposed between the particles, or by combinations thereof. For examples, see U.S. Pat. Nos. 3,136,615; 3,141,746; and 3,233,988. A supported abrasive particle compact herein termed a composite compact, is an abrasive particle compact which is bonded to a substrate material, such as cemented tungsten carbide. Compacts of this type are described, for example, in U.S. Pat. Nos. 3,743,489, 3,745,623, and 3,767,371. The bond to the support can be formed either during or subsequent to the formation of the abrasive particle compact.
Composite compacts have found special utility as cutting elements in drill bits. These compacts can be attached directly to the drill crown of drill bits by a variety of techniques. U.S. Pat. No. 4,156,329 proposes to furnace braze a pre-tinned metal-coated compact to recesses formed in the crown. U.S. Pat. No. 4,186,628 proposes to attach the compact cutters to the crown by placing the compacts in a mold, filling the crown portion of the mold with powder, and running a low temperature infiltration braze into the mold to form the crown containing the compacts embedded therein. U.S. Pat. No. 4,098,362 proposes drill bits in the manner of the latter proposal wherein the cutters are placed at a rake angle of between -10.degree. and -31 25.degree..
Alternatively, composite compacts can be affixed to an elongated stud or substrate which stud then is attached to the drill crown. The stud provides greater attachment area to the drill crown. It also provides more support for the abrasive particle compact thereby increasing its impact resistance. Composite compacts have been attached to studs in both a right cylinder configuration as depicted in U.S. Pat. No. 4,200,159, and in an angled configuration, as shown, for example, in U.S. Pat. No. 4,265,324.
Although the benefits of attaching a composite compact to a stud or substrate are apparent, problems have been encountered in achieving the actual attachment. In particular, it has been noted that composite compacts in which the abrasive portion is self-bonded and metal infiltrated such as described in U.S. Pat. No. 3,745,623 and available commercially under the trademarks Compax and Syndite are susceptible to thermal damage if exposed to temperatures in excess of about 700.degree. C. (As used herein self-bonded means that the abrasive particles are directly bonded one to another.) This damage is thought to result from a differential in the thermal expansion rate of the abrasive and metal phases. At elevated temperatures there is also a risk of degradation to the particles themselves as by graphitization or oxidation. This type of degradation is thought to be of concern for all types of diamond abrasive particle compacts. Accordingly, braze alloys with liquidus temperatures of less than 700.degree. C. were utilized initially for attachment of composite compacts to studs or substrates. Unfortunately, such low temperature braze alloys found only limited applicability in the marketplace due to their characteristically low bond strengths.
A major breakthough in the attachment of composite compacts to substrates was made by Knemeyer in U.S. Pat. Nos. 4,225,322 and 4,319,707. The Knemeyer process permits the use of high temperature braze alloys for attaching a composite compact to a substrate. Such high temperature braze alloys, in turn, provide significantly greater bond strengths. While the Knemeyer method and apparatus permit the use of high temperature braze alloys, difficulty has arisen in the selection of a suitable one. Preferred brazing alloys include the gold-based alloy disclosed in commonly-assigned U.S. Pat. No. 4,527,998 and the palladium-based braze alloy disclosed in commonly-assigned application Ser. No. 752,419, filed July 5, 1985. The braze filler alloys have a liquidus above 700.degree. C.
Another geometric configuration of the abrasive particle compact implemtns involves the use of a recessed or pocketed stud which receives the abrasive particle compact. Various adaptations of such pocketed studs can be seen in U.S. Pat. Nos. 4,452,324, 4,303,136, 4,221,270, 4,199,035, 4,098,362 and 4,373,410. One unifying characteristic of these proposals is that the stud ledge or land upon which rests the mated edge of the compact supports the entire thickness of support and abrasive particle layer and can extend beyond the abrasive particle layer.